Hardware Safety Guidelines For The PC Musician

PC Musician

Technique : PC Musician

The new PC interfacing standards of USB and Firewire brought with them the promise of 'hot-plugging' and easy interconnection. But some musicians have discovered, to their cost, that the reality doesn't always live up to the promise. We investigate.

Martin Walker

Did you know that it's quite possible to destroy your audio interface in an instant? It doesn't matter whether you have a budget £50 PCI soundcard or a top-of-the-range £1000 external Firewire interface, and you won't know that anything is amiss until the next time you try to power it up and wonder why nothing happens. Hardware problems can even result in your motherboard being partially 'fried', and replacing that can be far more long-winded than replacing an audio interface. If such a thing ever happens to you, you might be able to get the affected part replaced or repaired under your normal guarantee, but an external hard drive could fall prey to the same fate, and if that happened you might lose a lot of your own irreplaceable data as well.

Obviously, no hardware is indestructible, but the kind of calamities referred to above can usually be prevented if you follow certain straightforward guidelines that I'll cover in this article. So if you want to avoid expensive repairs and occasional glitches, as well as giving your computer and audio hardware the chance to perform at its best, read on...

Hot-plugging Problems

Let's start with potentially the most serious problem of all, since it can result in you having to replace your PC motherboard. I have mentioned this issue before in the pages of SOS, but many musicians still seem to be unaware of it or, even worse, under the false impression that it only applies to products from certain manufacturers. I'm talking about plugging in Firewire devices while your PC is already switched on. This 'hot-plugging' was one of the big attractions of Firewire, as it was with USB devices. Unfortunately, a few people with Firewire peripherals among the millions who use them have suffered disastrous consequences when doing this. They plug in their audio interface or external hard drive as normal, but it isn't recognised by the computer. Most people assume that the cable isn't making a good contact, so they pull it out and plug it in again, but this doesn't make any difference. They then try plugging in a different Firewire peripheral, but this isn't recognised either, and they often continue trying a variety of solutions, such as rebooting the computer, changing BIOS parameters, and so on. Eventually the dreadful truth dawns: the computer's Firewire port is no longer functioning at all. At this point there are two possible solutions: either buy a PCI Firewire card (or a PCMCIA one in the case of a laptop) to provide one or more replacement ports, or replace the entire motherboard.

Edirol have fitted extra protection circuitry on their FA101 and FA66 interfaces so that if they are hot-plugged without using the optional PSU there's a short pause before the power is applied. This should prevent hot-plugging damage, but not all Firewire devices are so equipped. It's generally safest to avoid hot-plugging Firewire devices whenever possible.

This problem was first brought to my attention by M Audio, and we should be very glad that they're doing their best to publicise it. Unfortunately, the good deed has backfired, with ill-founded rumours circulating that "M Audio FireWire devices can fry your motherboard". In fact, the same fate has befallen quite a few PC and Mac owners as a result of plugging in external hard drives, camcorders and CD burners, as well as audio interfaces from a variety of manufacturers. Although the motherboard port is usually the one affected, it has been known for the Firewire peripheral itself to be damaged, or for both motherboard and peripheral to be damaged (although these seem to be rarer scenarios).

So what causes the damage, and what precautions can you take to minimise the chances of you being one of the unlucky few that ends up with a fried port when hot-plugging?

One theory is that the user picks up the Firewire cable, walks across the carpet picking up an electrostatic charge (see 'Static Precautions' box for static advice) and then zaps the port when plugging the cable in. However, this seems unlikely: at no point do your fingers come into contact with the connections inside the Firewire plug, and even if you hold onto the metalwork of the Firewire plug itself, any static build-up should be safely discharged through the metal chassis of your computer when you plug it in.

A more likely scenario is that the user attempts or even manages to insert the Firewire plug the wrong way around — despite the keyed plugs, I've noticed that it's possible to push the plug part-way into the socket if you do so at an angle, and this is easier than you might imagine if the socket is at the back of your PC under the desk. It's even easier if either the socket or plug are worn, and the result is that the power contacts are shorted to the data lines, which could fry the port.

To avoid this happening, you should always replace any data cables that look as though they're getting worn out, and always take care to orientate the plug correctly before pushing it home. If the socket is out of sight, try using a small mirror or check your motherboard manual to see which way up the socket is mounted. Also, if you have problems mounting a Firewire device, first try it with a different cable rather than plugging in a different device, so that a faulty cable is ruled out and doesn't damage anything else that it's plugged into. A third possibility for the Firewire problem we're discussing is that the end of the cable has to be twisted through 180 degrees to mate it with the socket, and then this torque twists the contacts of the plug/socket internally, resulting in a short — so try to avoid such twisting if possible.

Most Firewire audio interfaces, like the Presonus Firestation shown here, provide a second Firewire port for daisy-chaining further devices, but not all manufacturers are agreed on whether this is a good idea.

The final possibility is the most worrying and concerns Firewire devices that are powered parasitically from the Firewire buss (AKA 'self-powered'). When you push the Firewire plug connecting such a device into the socket, the power is applied to it, resulting in a momentary startup spike appearing on its data output, which is then transmitted to the computer's port. If your self-powered Firewire device has a separate power switch, you can minimise the chances of this happening by plugging in the device and only then powering it up, so that all the connections are already properly made before power is applied. A further precaution might be to buy a cheap powered hub, so that if the worst happens you only have to replace the hub rather than the computer port.

M Audio and Tascam both recommend that all Firewire connections and disconnections be made with the power to both the device and the computer switched off, and while Edirol maintain that their interfaces can be hot-plugged, they still prefer that you avoid doing it regularly, 'just in case'. Firewire peripherals that have their own mains power supplies should normally be treated in the same way: plug them into your computer's Firewire port, then switch them on, then switch on your computer. However, there may be exceptions, so always follow any attachment and power-up advice given by the peripheral manufacturer.

Some recent PCs may have more robust Firewire ports incorporating better surge/spike protection, and some self-powered Firewire devices now have 'slow startup' protection circuits to eliminate surges when they are plugged in, but if you hot-plug, there is still a risk involved. If the worst happens to you and your PC or peripheral is still under warranty when one of its ports gets damaged, you shouldn't have any problems getting it repaired free of charge.

Before I conclude this section, I should also mention some completely contradictory advice I discovered during my researches. Many Mac OS X Panther users with external Firewire hard drives have apparently found them unusable after restarting their computers with the drive already connected, and are being advised to unmount them and unplug the Firewire cables from the Mac before powering down, to avoid sleep mode, and only to plug in the hard drives when the Mac is already running. This seems to be a completely different problem, related to a Mac operating system glitch (it only affects this particular OS revision), Furthermore, most Firewire drive manufacturers have subsequently released firmware updates to fix it. PC users and all other Mac users who haven't experienced this particular problem should leave their Firewire peripherals plugged in.

Digital Cable Quality Although most musicians take care to use good-quality audio cables for both studio and live work, to ensure reliability and minimum signal degradation, many will still plug in any digital cable that's long enough to do the job, without any further thought — after all, bits are bits aren't they? Well, while it's true that as long as all the bits get from one end of the cable to the other everything should be OK, in practice there are some limitations, largely because the digital waveform starts to degrade due to cable capacitance, and the initially sharp transitions from high to low levels become blurred and their timing more uncertain. The most critical cable is one connected to a D-A converter, because any jitter here will smear the audio timing, resulting in an unfocused sound, so you should always keep this cable as short as possible. If a sufficiently long digital cable is used, eventually you'll start to get errors in your data. Every digital standard tends to have an associated maximum length of cable associated with it, and USB and Firewire are no exception. Here are the maximum recommended lengths for various digital cables that will be of interest to musicians: Firewire: 4.5 metres (14.74 feet). USB: 5 metres (16.4 feet). S/PDIF: 10 metres (32.75 feet with 75(omega) impedance unbalanced cable and phono connection) TOSlink: 15 metres (49.1 feet using optical cables). AES3: 100 metres (327.5 feet with 110(omega) impedance balanced cable and XLR connection). If, for any reason, you need longer cables, the correct way to increase cable reach is using 'repeaters' that clean up and boost the signal and pass them onto the next stage in the chain. Most USB and Firewire audio interfaces are bundled with suitable high-quality digital cables, but it's easy to get these mixed up with bargain-basement alternatives unless you're careful. For instance, USB 1.1 cables can theoretically be used with a Hi-Speed USB 2.0 device, but when USB 1.1 products first appeared, sub-standard cables were churned out at low prices. Since USB 2.0 cables must handle a much wider bandwidth than their USB 1.1 counterparts (480 Megabits per second compared with 12 Megabits per second), if you've got a Hi-Speed USB peripheral always use the cable that came with it, which will have a braided shield and twisted-pair conductors. This should be clearly marked USB2 somewhere along its length, or on a tag.

Daisy-chaining

One of the benefits of the Firewire format is that you can daisy-chain several devices to a single computer port, by connecting the first in the chain to the computer, the second to the spare Firewire port on the rear panel of the first device, and so on. Indeed, many audio interfaces have two identical Firewire ports on their back panels for just this purpose, and many musicians use them to add an external hard drive to the end of their Firewire chain, specifically for audio recording. This means that you don't have to buy a 'hub', which provides several extra ports in one convenient package, to plug into your PC (more later on hubs).

Don't get fooled into buying a 'Full-Speed USB' device, such as a scanner or printer, that only runs at 12Mbps. Look for the red Hi-Speed flash that signifies a true 480Mbps peripheral.

The theoretical limit to the number of chained devices is 64, but unfortunately some people run into problems long before this. Such problems range from devices not being recognised (either occasionally, not at all, or only if in a certain position in the chain) to the computer refusing to boot up until one or all of the devices in the chain are switched off or removed. During my research I found a few common scenarios: for example, external CD-R/W or DVD-R drives are often not recognised when they're connected at the end of a chain containing external hard drives. Most problems seem to be connected with 'enumeration'. When you plug in a device, the enumeration process assigns a unique address to it for data transfers, and also identifies which driver needs to be loaded. Long chains seem to confuse the process, so if this happens to you try changing the device order or (preferably) spreading the Firewire devices across several computer ports.

There's also the question of Firewire bandwidth. While Firewire 400 supports a maximum transfer rate of 50MB/second (400 Megabits/second), it can be difficult to predict how several devices will jockey for position and interfere with each other's instantaneous requirements when they are chained together. The theoretical 400Mbps limit may also prove to be considerably lower in practice, so it's important to make the most of what there is. Remember also that when you chain a Firewire audio interface and hard drive, the data being recorded is not only being sent from the interface to your PC, but also back down the same Firewire cable past the interface and on to the hard drive, so this is likely to reduce the maximum number of simultaneous audio tracks you can record.

Each USB Universal Host Controller is in charge of a pair of USB ports, so it pays to organise your USB devices to make the most of each controller's bandwidth (see text on next page).

Unfortunately, there's a lot of conflicting advice, even from the interface manufacturers. MOTU could be said to have invented Firewire audio interfaces and their users regularly chain several powered interfaces to run huge numbers of simultaneous audio tracks, subject only to the maximum Firewire bandwidth available. However, they don't recommend daisy-chaining Firewire buss-powered devices, to avoid overloading the buss.

Terratec also say in their Phase 88 Rack FW documentation that "hubs are superfluous as long as the cable length between the individual devices does not exceed 4.5 metres or a total of 72 metres, as this would cause problems due to signal attenuation". However, they go on to say that there are a number of stumbling blocks, such as camcorders that do not comply with IEEE 1394 and transmit their data without consideration of standards or potential losses, and that a complex audio production may consume the entire Firewire transfer rate all by itself. Other manufacturers are more cautious. For example, Tascam's FW1804 manual states that it is "a high-bandwidth device and chaining other devices with it will very likely degrade its performance or the performance of the other devices".

So how should you connect up your hard drive and interface? Well, although some say that the audio interface should always be plugged directly into the computer, and any Firewire hard drive plugged into that, I don't think there are any hard and fast rules. Anyone who is struggling to run more than half a dozen audio tracks without glitches may find that the problem is down to the Firewire chipset in the PC: TI (Texas Instruments) and Lucent chipsets are widely recommended as the most compatible, but NEC are not. In this case, buying a PCI-to-Firewire adaptor card may solve the problem cheaply.

If you ever exceed the available Firewire bandwidth, one of your connected devices will temporarily disappear from the chain and your sequencer is likely to stop with an error, such as a non-existent external hard drive. However, some users are successfully running 80-in/80-out setups at 24-bit/44.1kHz using chained Firewire interfaces before this happens, which proves just how capable Firewire can be with the right components.

Static Precautions I suspect that almost everyone has experienced the effects of an ESD (Electrostatic Discharge), either from wearing man-made fibres (nylon socks, for instance) or walking across a carpet made from similar materials and grabbing a doorknob, or stepping out of a car on a hot, dry day. The voltage generated can easily be in excess of 10,000 — enough to give effects from a mild tingle to an unpleasant 'spark' — but since the current is so small these effects are rarely dangerous to our health. Unfortunately, even though you can't feel them, static discharges as low as 400V can damage electronic equipment, and can even cause fires and explosions if combustible gases are nearby. Indeed, ESD is estimated to cost businesses millions of pounds each year. You may not immediately destroy a component, either — a partially functioning RAM stick, for example, may not show any noticeable effects for a long time and can be very difficult to diagnose. All electronics manufacturers take precautions to minimise such damage, such as adding protection circuitry at vulnerable points, but when you're installing a new motherboard, processor, graphics card, PCI soundcard or extra RAM you should always follow these precautions: If the card comes in anti-static packaging, leave it there until just before installation. If you're supplied with a disposable anti-static wristband, use it: connect yourself to an earthed object (normally the chassis of your PC) so that you can't build up a static charge. If not, touch an earthed metal object such as a radiator or your outboard rack before starting work, to safely discharge any static buildup, and do so periodically during the install, particularly if you've moved your feet. Make sure your computer has not only been switched off by the front-panel power switch, but also by the rear-panel mains switch. Most motherboards remain on standby power until this second step, indicated by an illuminated LED somewhere on the board. Some experts also advise removing the PC's mains cable as well, although this also removes the earth connection from the PC chassis, so the safest approach is to switch the mains power off at the wall socket but leave the lead plugged in. When handling the device, always keep your fingers away from its contacts (the edge connector in the case of an expansion card, for instance), and try to hold the item by any exposed metalwork, such as the backplate of an expansion card, or the case of a hard drive. Don't remove items of clothing during installation (and particularly don't pull a jumper over your head), as this could generate high electrostatic levels, and don't roll about on your office chair, as this is also a prime culprit. Worst of all, never let your cat anywhere near your computer when working on it. Cats are walking balls of static!

USB Problems

Of course, it isn't only Firewire audio interfaces that can run into problems: the Universal Serial Buss has also had its fair share of 'issues', particularly in the early days of its much slower USB 1.1 incarnation (12 megabits/second in high-speed mode and 1.5 megabits/second in low-speed mode), when some USB motherboard chipsets caused frustrating audio click and pop problems. Fortunately, the much more capable USB 2.0 chips fitted on most modern PC motherboards not only have a hugely increased maximum transfer rate (480 megabits/second, or 60MB/second), but they have also resolved the vast majority of glitch-related issues, even when you plug in older USB 1.1 devices.

If you want to ensure a steady power supply to your USB audio and MIDI devices, un-tick this box for each USB Root Hub connected to them.

USB 1.1 devices remain fully compatible with USB 2.0 ports and continue to work perfectly well within their limits, and there are still plenty of USB 1.1 MIDI interfaces being sold, as well as lots of budget stereo audio interfaces that run perfectly well at up to 24-bit/48kHz. Unfortunately, the arrival of USB 2.0 resulted in far fewer USB 1.1 devices being sold, so the powers that be decided to rename the two USB 1.1 modes as Full-Speed USB and Low-Speed USB, with bespoke USB 2.0 peripherals becoming Hi-Speed USB. So, if you're about to buy a USB peripheral, try not to get caught out buying a 12Mbps device when you thought it was a 480Mbps one! Most audio interface manufacturers are not guilty of confusing their potential customers, but you might be fooled when buying a scanner or printer, so look for the red 'Hi-Speed' flash on the logo.

The vast majority of PCs now offer USB 2.0 ports, which you can normally recognise in Device Manager by the fact that the word 'enhanced' appears somewhere in the list of Universal Serial Buss controller entries. My Asus P4P800 Deluxe motherboard supports up to four pairs of USB 2.0 ports, and I can decide in the BIOS settings how many of these ports are activated (two, four, six or eight). As with many motherboards, only the first two pairs actually have physical USB sockets on the rear panel, so if you require more than this you may need to buy a USB header cable with an attached backplate for each additional pair of USB ports.

If you look inside Device Manager and select the 'Devices By Connection' option in the View menu, you'll see that there is a number of Universal Host Controllers, each one of which has its own self-powered USB Root Hub that provides a pair of USB ports. Each of the last can supply up to 500mA of power to USB devices plugged into them.

If you run out of USB ports, buying a powered hub such as the Belkin one shown here will minimise potential problems by providing sufficient power for each device plugged into it.

Each USB Controller has a fixed amount of bandwidth, which all attached devices must share, so the key to extracting the best possible performance from your USB audio and/or MIDI interfaces and external USB 2 hard drive is to make sure they are all connected to different controllers. As each controller is connected to a pair of ports, this means plugging your audio interface into either port belonging to one pair, your MIDI interface into either port of another pair, and so on. This will distribute the load. Even multi-port MIDI interfaces don't, by themselves, take a lot of bandwidth compared with the total available, but if they're fighting for bandwidth with a multi-channel audio interface running multiple channels of 24-bit/96kHz on the same controller, their timing may suffer or the audio may glitch.

Another consideration is whether you're connecting both USB 1.1 and USB 2.0 devices to the same controller chip. Since USB is a serial standard (ie. the data is sent one bit after the other), the controller will poll one device and then the other, and you can imagine the consequences for the 480Mbps device if the controller spends half its time switched to 12Mbps to check the slower one. If the faster device has drivers that use 'isochronous' mode, it can take as much bandwidth as it needs and leave the other one whatever is left over, but this could mean that the slower device is left with less bandwidth than it had before, resulting (for instance) in great audio performance but an extremely sluggish USB mouse.

Occasionally, intermittent USB device problems can be tracked down to Power Management issues. Windows is normally allowed to turn off devices to save power if no activity has been detected for some time, but you can disable this feature to ensure steady power delivery to selected devices, especially if you know that they either have minimal power requirements or their own dedicated PSU. Open Device Manager, and for each of the USB Root Hubs that are being used to connect audio/MIDI devices, un-tick the box labelled 'Allow the computer to turn off this device to save power' (see the screenshot on page 105).

By the way, chained Firewire devices will interfere with each other's performance far less than USB devices, because although there are several Firewire connection speeds, the fastest is 800Mbps and the slowest 100Mbps, a ratio of only 8:1. Between 480Mbps and 12Mbps for USB the ratio is 40:1 — and it's 320:1 if a 1.5Mbps USB device is involved.

Unusual USB/Firewire Problems Occasionally a particular USB 2.0 device won't work with one computer, but will with another — I've had this happen myself with a particular USB 64MB Flash Drive, which worked fine with my laptop but immediately threw up a 'USB Device Not Recognised' error message whenever I plugged it into my desktop PC. This may be because the device does not completely conform to USB standards or pushes them to the limit. Sometimes you can cure such problems by installing updates for the motherboard chip set drivers, or updating the motherboard BIOS, but sometimes the only solution is to buy a USB 2.0 expansion card and use its ports instead. If every single one of your USB ports suddenly fails to operate, but the USB Host Controller entries are all still showing up in Device Manager, it may be due to another incompatibility. I've heard of this situation arising when someone using a motherboard with built-in AGP support installed a more capable AGP graphics card without disabling the previous one in the BIOS.

The Hub Of The Matter

USB devices can't be daisy-chained, so if you run out of ports you should ideally buy a PCI card featuring another host controller that supports two or more additional USB ports. Failing that, some sort of hub, which plugs into one of your existing ports but provides two, four, or more ports of its own, can be used. Such a hub won't provide any more bandwidth, as all its ports will still be sharing the same host controller chip on your PC that the hub is plugged into, but it will certainly provide you with plenty more ports.

When daisy-chaining Firewire devices, you need to be careful not to exceed the total bandwidth available, and not all device combinations will work successfully. However, just to prove what a single Firewire port can manage, up to four MOTU 828 MkII interfaces can be daisy-chained for up to 80-in/88-out operation at 44.1/48kHz sample rates.

Nowadays it's best to buy a USB 2.0 hub, since they support all device speeds, with their more sophisticated chip set logic. However, if you already have a USB 1.1 hub it can still be used, although all devices you plug into it will be capped at the much slower USB 1.1 speed. A USB 2.0 hub will also work fine when plugged into an older USB 1.1 port, but it will also be demoted to USB 1.1 performance.

Each USB port has four connections: one connection for ground, two for data and one for +5V power. The cheapest hubs are 'self-powered', relying on this 5V connection not only for their own power, but also to provide any power that's required for the devices you plug into its ports. Most hub problems are encountered with this self-powered variety, simply because they cannot provide enough power for the devices that are connected to them.

As an example, a single USB port can supply up to 500mA to external devices. However, if you plug a four-way self-powered hub into it, this 500mA must, in turn, be shared between the four devices that you plug into the hub. Depending on what you connect, it may work or it may not (powered desktop speakers are usually early casualties). So if you must use a self-powered hub, try to restrict it to connecting devices that include their own power supplies, or those that you know are likely to draw only a small current.

A hub with its own power supply, although more expensive, can always provide the full 500mA from each and every one of its ports, which resolves the majority of hub problems. However, I have come across a few isolated reports of single devices not liking being alone on a powered hub — and, ironically, the solution to this problem is sometimes to unplug the hub's PSU! Another possible problem is that the hub isn't correctly identifying devices plugged into it (enumeration again). This might be due to a faulty hub, or your PC might not be recognising the hub properly. If the hub was supplied with its own drivers, they may need to be installed to solve the problem.

USB hubs can be cascaded to provide yet more ports, but there are performance implications when you do this. No more than two hubs should be cascaded, and if you need more ports it's really better to buy a hub that has enough ports to supply your needs without having to be cascaded, or to make sure that if you definitely do need multiple hubs, each one is directly connected to a different USB controller on your PC.

If possible, keep your USB audio interface plugged into its own dedicated PC port to give it the best possible chance of performing well. Digidesign actually specifically state that connection of their M Box interface to a USB hub is not supported, and some other types of USB device are also known to dislike hubs, including cameras, scanners and hard drives, so try to give these a dedicated port as well. If you need to use a USB hub, there are lots of myths surrounding the best make and model to buy, but models from Belkin, Adaptec and Gefen seem to be widely recommended.

Published in SOS October 2005